Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/01—Manufacture or treatment
  • H10N60/0268—Manufacture or treatment of devices comprising copper oxide
  • H10N60/0661—Processes performed after copper oxide formation, e.g. patterning
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/01—Manufacture or treatment
  • H10N60/0884—Treatment of superconductor layers by irradiation, e.g. ion-beam, electron-beam, laser beam or X-rays
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N60/00—Superconducting devices
  • H10N60/01—Manufacture or treatment
  • H10N60/0912—Manufacture or treatment of Josephson-effect devices
  • H10N60/0941—Manufacture or treatment of Josephson-effect devices comprising high-Tc ceramic materials
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S505/00—Superconductor technology: apparatus, material, process
  • Y10S505/725—Process of making or treating high tc, above 30 k, superconducting shaped material, article, or device
  • Y10S505/73—Vacuum treating or coating
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S505/00—Superconductor technology: apparatus, material, process
  • Y10S505/725—Process of making or treating high tc, above 30 k, superconducting shaped material, article, or device
  • Y10S505/73—Vacuum treating or coating
  • Y10S505/731—Sputter coating
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S505/00—Superconductor technology: apparatus, material, process
  • Y10S505/725—Process of making or treating high tc, above 30 k, superconducting shaped material, article, or device
  • Y10S505/73—Vacuum treating or coating
  • Y10S505/732—Evaporative coating with superconducting material

Definitions

• the present invention relates to a process for depositing a thin film on a thin film of oxide superconductor, more particularly, to a process for improving crystallinity of a surface of the thin film of oxide superconductor so that another thin film grows epitaxially on the surface of oxide superconductor.
• a superconducting compound oxide of (La,Sr) 2 CuO 4 which exhibits the superconductivity at 30 K. was discovered in 1986 by Bednorz and Muller (Z. Phys. B64, 1986 p 189). Then, another superconducting material of YBa 2 Cu 3 O 7- ⁇ having the critical temperature of about 90 K. was discovered in 1987 by C. W. Chu et al. (Physical Review letters, Vol. 58, No. 9, p 908) and Maeda et al discovered so-called bismuth type superconducting material of Bi--Sr--Ca--Cu--O (Japanese Journal of Applied Physics, Vol. 27, No. 2, p 1209 to 1210). The other high-temperature compound oxide systems are also reported.
• These superconducting compound oxides are expected to be utilized in electronics devices such as Josephson element or superconducting transistors due to their high critical temperatures (Tc).
• Tc critical temperatures
• tunnel type Josephson Junction having a layered structure of superconductor/non-superconductor/superconductor, at least three layers of a thin film of the first superconductor, a thin film of the non-superconducting and a thin film of the second superconductor must be deposited successively on a substrate.
• a thickness of the non-superconductor layer is determined by or depends on the coherent length of superconductor used.
• the thickness of the non-superconductor layer must be as thin as several nanometers (nm) because the coherent length of oxide superconducting is very short, so that it is requested to prepare a very thin film of non-superconductor.
• such very thin film of non-superconductor must have good crystallinity of high quality.
• all thin film layers of superconductor/non-superconductor/superconductor have good crystallinity of high quality and are preferably made of single crystals.
• the resulting Josephson Junction including such polycrystal or amorphous thin film layer(s) shows poor performance and, in the worst case, does not work.
• the thin films having good crystallinity of high quality are also required in a process for fabricating the superconducting transistors in which superconductor is combined with semiconductor.
• first thin film of oxide superconductor deposited When a first thin film of oxide superconductor deposited is exposed to air, both of superconductivity and crystallinity are deteriorated or lost to a depth of about 1 nm at a surface of the first thin film.
• the deposited first thin film of oxide superconductor is inevitably exposed to air, because deposition of the first thin film of oxide superconductor (for example, prepared by sputtering) and deposition of another thin film to be layered thereon (for example, prepared by vacuum evaporation) are carried out in different chambers, so that the first thin film of oxide superconductor is necessarily exposed to air during transportation from one chamber to another chamber.
• the first thin film of oxide superconductor is heat-treated at about 700° C. in ultra-high vacuum of about 1 ⁇ 10 -9 Torr before another thin film is deposited thereon. It is true that this heat-treatment improves crystallinity of the surface of the first thin film of oxide superconductor and hence the upper thin film to be deposited thereon can be grown epitaxially.
• the superconducting property may be maintained if the heat-treatment is carried out in oxygen atmosphere. In this case, however, crystallinity of the surface of the first thin film of oxide superconductor can not be improved or becomes worse.
• an object of the present invention is to solve the problems and to provide a process to improve crystallinity of the surface of the first thin film of oxide superconductor on which another thin film is to be deposited without spoiling superconducting property of the first thin film.
• the present invention provides a process for depositing another thin film on a first thin film of oxide superconductor deposited previously on a substrate, a characterized in that a surface of the first thin film of oxide superconductor is irradiated with laser beam pulses in high-vacuum of lower than 1 ⁇ 10 -6 Torr, preferably lower than 1 ⁇ 10 -8 Torr, before another thin film is deposited thereon.
• the heat-treatment should be effected in vacuum of lower than 1 ⁇ 10 -6 Torr. If the vacuum is not lower than 1 ⁇ 10 -6 Torr, improvement in crystallinity of the thin film of oxide superconductor can not be obtained.
• Laser beam pulses used in the present invention are preferably high-power laser beam pulses, each pulse having a very short unit emission time such as excimer laser pulses.
• a surface of the thin film of oxide superconductor irradiated with the laser pulses is heated instantaneously and then is cooled within a very short time duration.
• heated means that the thin film is irradiated with energy of any form.
• crystallinity of the surface of the first thin film of oxide superconductor is improved in the same manner as prior art but, contrary to the prior art, oxygen inside the first thin film of oxide superconductor does not diffuse and is not lost because heating is effected instantaneously within a very short time. From this fact, the first thin film of oxide superconductor thus treated maintains good superconducting property and also possesses improved crystallinity. Therefore, another thin film such as non-superconductor which will be deposited on the first thin film of oxide superconductor thus treated can be grown epitaxially.
• Laser beam pulses used in the present invention have preferably the energy density per one pulse of 0.01 to 0.1 J/cm 2 .
• the energy density per one pulse which is not higher than 0.01 J/cm 2 is too low to improve the crystallinity of the thin film of oxide superconductor. To the contrary, if the energy density per one pulse exceeds 0.1 J/cm 2 , the thin film of oxide superconductor will be damaged.
• the number of laser pulses which are directed onto the thin film of oxide superconductor is determined in the function of various factors including the energy density, incident angle and surface condition of the thin film to be treated.
• the number of laser pulses directed onto one spot on the thin film of oxide superconductor is selected preferably between 100 pulses and 1 pulse.
• irradiation of laser pulses is preferably adjusted by monitoring an irradiated area of the thin film of oxide superconductor by a reflective high energy electron diffraction (RHEED) analyzer, low density electron diffraction (LEED) analyzer or the like.
• RHEED reflective high energy electron diffraction
• LEED low density electron diffraction
• irradiation should not be repeated continuously in a short interval in order not to elevate temperature of an irradiated spot of the thin film to such a high value that oxygen escapes out of crystal.
• the first and second thin films of oxide superconductors used in the process according to the present invention can be any known oxide superconductor including Y--Ba--Cu--O system such as Y 1 Ba 2 Cu 3 O 7-x (x is ⁇ 1), Bi--Sr--Ca--Cu--O system such as Bi 2 Sr 2 Ca 2 Cu 3 O x (x is about 10) and Tl--Ba--Ca--Cu--O system such as Tl 2 Ba 2 Ca 2 Cu 3 O x (x is about 10).
• Y--Ba--Cu--O system such as Y 1 Ba 2 Cu 3 O 7-x (x is ⁇ 1)
• Bi--Sr--Ca--Cu--O system such as Bi 2 Sr 2 Ca 2 Cu 3 O x (x is about 10)
• Tl--Ba--Ca--Cu--O system such as Tl 2 Ba 2 Ca 2 Cu 3 O x (x is about 10).
• Y 1 Ba 2 Cu 3 O 7-x is preferable because thin films of high quality are obtainable stably and Tl 2 Ba 2 Ca 2 Cu 3 O x is also preferable due to its high critical temperature (Tc).
• the first and second thin films of oxide superconductors and the non-superconductor layer can be prepared by sputtering technique. Operational condition of sputtering itself is known.
• the thickness of the first thin film of oxide superconductor is not limited specially but has preferably a thickness of 20 to 3,000 ⁇ , more preferably between 100 to 2,000 ⁇ . If the thickness is not thicker than 20 ⁇ , it is difficult to prepare a uniform thin film layer. Thicker thin film over 3,000 ⁇ may not improve substantially the properties of the first thin film of oxide superconductor and will be a cause of inter-diffusion between substrate material and oxide superconductor.
• the above-mentioned another thin film can be made of any non-superconducting material and has preferably a crystal structure and/or lattice constants which are similar to that of oxide superconductor of which the first and second thin films are made.
• the non-superconductor can be made of BaF 2 and oxides such as MgO, SrTiO 3 or the like.
• the thickness of the non-superconductor depends on the coherent length of oxide superconductor used and is in the order of several nanometers (nm).
• a second thin film of oxide superconductor is deposited further on the thin film of non-superconductor.
• the second thin film of oxide superconductor can be prepared by the same manner as the first thin film of oxide superconductor.
• the second thin film of oxide superconductor can be grown epitaxially on the thin film of non-superconductor prepared by the present invention because the later thin film possesses good crystallinity.
• a well-crystalline thin film of non-superconductor can be prepared on a thin film of oxide superconductor and hence the tunnel type Josephson Junction can be realized from high-temperature oxide superconductors.
• a Josephson Junction was produced on a substrate of MgO by depositing a first thin film of oxide superconductor, a thin film of BaF 2 as a non-superconductor and a second thin film of the same oxide superconductor as the first thin film successively in this order.
• Operational conditions used for preparing the first thin film of oxide superconductor are as following:
• the resulting substrate having the first thin film of oxide superconductor was transferred from a sputtering chamber to a vacuum evaporation chamber and then a surface of the first thin film of oxide superconductor was irradiated with laser pulses under the following conditions:
• the laser beam was scanned so that laser beam pulses were directed onto different spots on a surface of the first thin film of oxide superconductor.
• the number of laser pulses was determined by monitoring the surface by LEED such a manner that the first thin film of oxide superconductor shows good crystallinity.
• the critical temperature (Tc) of the first thin film of oxide superconductor was 85 K.
• Example 1 was repeated except that the thickness of the first thin film of oxide superconductor was changed from 300 nm to 200 nm, the thickness of the non-superconductor thin film of BaF 2 was changed from 5 nm to 3 nm and that following operation was continued.
• the critical temperature (Tc) of the second thin film of oxide superconductor determined by the same method as Example 1 was 80 K.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Superconductor Devices And Manufacturing Methods Thereof (AREA)
• Superconductors And Manufacturing Methods Therefor (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)

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• 1991
  • 1991-07-12 US US07/728,212 patent/US5234901A/en not_active Expired - Fee Related
  • 1991-07-12 EP EP91401953A patent/EP0466607B1/fr not_active Expired - Lifetime
  • 1991-07-12 CA CA002047001A patent/CA2047001C/fr not_active Expired - Fee Related
  • 1991-07-12 DE DE69115775T patent/DE69115775T2/de not_active Expired - Fee Related

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